The present invention relates to a method of forming a capacitor with reduced leakage current, and more particularly, to a method of oxidizing a capacitor dielectric layer so that leakage current across the conductive layers of the capacitor is reduced while capacitance is substantially unaffected. The invention also relates to the capacitor structures formed according to the various embodiments of the method herein set forth.
FIG. 1 illustrates a semiconductor device 110 containing a planar capacitor structure 114 formed over a substrate 112. The structure of FIG. 1 is not intended to represent a particular capacitor as constructed in a semiconductor device, but is merely used as an example to illustrate the main components of such a capacitor. Substrate 112 may be formed, for example, of silicon or silicon-on-insulator (SOI) material or other well known substrate material. A first conductive layer or bottom electrode 116 is formed over the substrate using materials and methods known in the art. For example, the first conductive layer may be formed of two layers: a polysilicon bottom layer with a hemispherical silicon grain, or HSG, layer atop the polysilicon.
The capacitor structure 114 may be coupled to an active region 113 in the substrate, for example a source or drain region of a MOS transistor. Alternately, the capacitor structure 114 may be insulated from the substrate 112 through an insulating region. A capacitor dielectric layer 118 is formed over the conductive layer 116, and may be formed of a substantially nonconductive material such as, for example, silicon nitride (Si3N4), or other dielectric material known in the art. A thin protective layer 119 is then formed over the dielectric layer using gaseous oxygen and hydrogen. The protective layer may thus comprise silicon dioxide (SiO2) which forms as the oxygen reacts with the silicon from the silicon nitride in the dielectric. The protective layer serves to xe2x80x9chealxe2x80x9d any defects in the dielectric layer 118 which might cause leakage problems across the resulting capacitor. A second conductive layer or top electrode 122 is formed over the protective layer and may be formed with polysilicon or other conductive material.
In order to effectively utilize the capacitor 114 in modern dynamic random access memories (DRAMs), however, it has been necessary to reduce its size and substantially minimize the thickness of the dielectric layer 118. In many embodiments, it is therefore especially desirable that the dielectric layer be less than about 60 Angstroms in thickness, and even more desirably, less than about 50 Angstroms thick. Unfortunately, leakage current between the first and second conductive layers 116, 122 tends to increase exponentially as the thickness of the dielectric layer 118 is reduced to below 50 Angstroms. While formation of the protective layer 119 has been instrumental in helping to reduce this leakage current, there is still considerable need for a further reduction to enhance overall capacitor performance, as capacitor sizes continue to shrink in memory devices.
What is therefore needed in the art is a new method of forming a capacitor structure which results in reduced leakage current, while overall capacitance is substantially unaffected. Also needed are new capacitors in which leakage current between conductive layers is minimized, while capacitance is substantially maintained.
The invention provides a method of forming a capacitor in a semiconductor device in which a first layer of conductive material is first formed, a second layer of a dielectric is formed over the first layer, the second layer is then contacted with hydrogen, oxygen and nitrous oxide gases to form an oxidation layer over the second layer, and a third layer of conductive material is then formed over the second layer. The resulting structure exhibits a lowered current leakage with little loss of capacitance when compared with similar capacitor structures in which the dielectric is built with a conventional hydrogen and oxygen treatment which forms an oxidation layer on the dielectric.
The invention further provides a method of oxidizing a capacitor dielectric by contacting it with hydrogen, oxygen and nitrous oxide gases to form an oxidation layer thereon. Other suitable gases would include those with an O (oxygen) or F (fluorine) moiety that bonds strongly to silicon.
The invention also provides a method of oxidizing a capacitor dielectric which involves adding an oxygen containing gaseous material (e.g., nitrous oxide) to a mixture of oxygen and hydrogen gases, and then contacting the capacitor dielectric with the gaseous mixture so as to form an oxidation layer over the capacitor dielectric. The thus processed dielectric has a lower leakage current than does the same dielectric having an oxidation layer formed by contacting the dielectric with only hydrogen and oxygen gases under the same reaction conditions.
The invention also provides a method of forming a capacitor dielectric over a substrate in which a layer of silicon nitride is deposited over a conductive layer which has first been formed over a substrate. The silicon nitride layer is then contacted with hydrogen, oxygen and nitrous oxide gases so as to form an oxidation layer thereon.
The invention also provides a method of oxidizing a dielectric layer of capacitor in an intermediate stage of fabrication in which the dielectric layer is exposed to a combination of hydrogen, oxygen and nitrous oxide gases, and the flow rate of the nitrous oxide gas is increased during oxidation while the flow rate of the hydrogen and oxygen gases are maintained substantially constant. The gas ratio of nitrous oxide to hydrogen and oxygen can be varied by either changing the nitrous oxide gas flow rate while keep the hydrogen and oxygen flow rates constant, or vice versa.
The invention also provides a semiconductor device having a substrate with at least one capacitor formed thereover. The capacitor includes first and second conductive layers, with a dielectric between these two layers which has been oxidized in the presence if by hydrogen, oxygen, and nitrous oxide gases to produce an oxidation layer over the dielectric.
The invention further provides a memory cell of a semiconductor device which includes a container capacitor. The capacitor has first and second conductive layers, a dielectric layer between the conductive layers and an oxidation layer over the dielectric layer. The oxidation layer is formed by an oxidation of the dielectric layer in the presence of a combination of hydrogen, oxygen and nitrous oxide gases.
The invention further provides an integrated circuit which includes at least one capacitor formed over a substrate, wherein the capacitor contains a first conductive layer, a dielectric layer over the conductive layer, an oxidation layer over the dielectric layer, and a second conductive layer over the dielectric layer. The oxidation layer is formed by an oxidation of the dielectric layer in the presence of a combination of hydrogen, oxygen and nitrous oxide gases.
The invention also provides a processor based system which includes a processor, and an integrated circuit device coupled to the processor. At least one of the processor and the integrated circuit device contains a capacitor which includes first and second conductive layers, a dielectric layer between the conductive layers and an oxidation layer over the dielectric layer. The oxidation layer is formed by an oxidation of the dielectric layer in the presence of a combination of hydrogen, oxygen and nitrous oxide gases.